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-   -   Question about "old" technology: the wiiide baffle of the Boston Acoustics "A" series (http://www.diyaudio.com/forums/multi-way/199856-question-about-old-technology-wiiide-baffle-boston-acoustics-series.html)

River757 4th November 2011 07:53 PM

Question about "old" technology: the wiiide baffle of the Boston Acoustics "A" series
 
Besides being a fan of BA speakers (before their takeover by D&M) this series of large floorstanding speakers, equipped with a 10" acoustic-suspension woofer, sold during much of the 1980s has always intrigued me because of their very wide baffles. IIRC those baffles were employed to better "launch" the sound waves from the tweeter, and midrange if so equipped.

I fully realize such a design is not "commercially viable" nowadays and its WAF is very low, but I don't care about either of those issues (though I do think they look pretty cool ;)). I just want to know if there are any sonic advantages to using a wide baffle for the floorstanders I am considering building.

Thanks!

Since there is now a new "A" series that just debuted (typical narrow tower, dual small woofers etc etc), finding pics of the originals became more difficult, so here are some I found myself:

A100 - 2-way version* (I don't know this guy - I'm just using his page for reference sake)

A150 - 3-way version

A200 - "up scale" 3-way version. The woofer, which is different than the other A series' woofers, is mounted much lower in this model (the speaker pictured on the left is equipped with the original version); there is a later model equipped with dual 8" woofers

* I think this version is the most elegant: because of its simple 2-way design and its clean styling with pleasing ratios. And a version with black woodgrain - NOT black gloss paint - I think would look even better.

454Casull 4th November 2011 08:59 PM

Yes.

With a large baffle, BSC is required only for a smaller portion of the bass spectrum, if at all, and therefore the power response attained from true half-space radiation is uniform for a wider range of the audible frequency spectrum. Power requirements will go down.

The drawbacks are:

1) ugly (usually)
2) the transducing elements (cones/domes) are small compared to the baffle and therefore will effect larger dips and peaks in the response due to baffle diffraction until such frequencies where beaming occurs. This can be modeled in various software such as Edge. Putting the drivers off-center, or better yet, using sizeable amounts of foam/felt/fiberglass to attenuate the waves traveling along the baffle, will reduce this effect.

Wide-baffle speakers (some people call them monkey coffins) are just a hop and skip away from in-wall systems, which tend to have much better power response than typical 2/3-way narrow floorstanders.

AllenB 4th November 2011 11:31 PM

The change in directivity index is brought closer the the Schroeder frequency (at least that's the way I've been looking at it). I've had a penchant for wider baffles for decades and feel it is one way to achieve a more balanced bass/mid region.

chris661 4th November 2011 11:46 PM

Here's something I posted in another thread that seems to be of relevance here too.

Quote:

Originally Posted by chris661
When a wave from the driver goes across the baffle, the edges diffract the sound, acting as a secondary sound source, with a small delay between the output from the edge and the driver itself.

If your system has a balance control, sit much closer to one speaker than the other, then adjust the balance so you can hear both speakers. Note there's still not much of a stereo image.
The reason for this, so far as I can tell, is that stereo imaging also needs low-level delayed signals, such as room ambiance.

When you have these wide baffles, you get a delay that's constant for each instrument (assuming a single driver, centred on a baffle), as well as the varying delays in the recording to indicate room position. This has to screw up the imaging at least a little.

Angling the edges reduces the actual output from the baffle edge, as well as making the baffle narrower, so these delays won't have so much effect. The narrow baffle has a delay so small that you'd simply think it was from the driver.

Chris

Hope this helps.

bbggg 5th November 2011 12:21 AM

Quote:

Originally Posted by River757 (Post 2770088)
such a design is not "commercially viable" nowadays and its WAF is very low

Yes, but see Troel's take on a Sonus Faber:
Poor Man'
Admittedly a curved baffle is tricky to make. I guess it can be done with Corian, for a price. I'm not sure what the deal is about steam-bending plywood either.

David Gatti 5th November 2011 12:32 AM

I owned the Boston A100s in the mid eighties and have fond memories of them. They were my first "hi-fi" speaker and were my inspiration for my latest project.

The main advantages I have found with the wide baffle is a better presentation of bass, especially male voices, and better efficiency (less baffle step compensation required).
Also if you are in a situaiton where you HAVE to put your speakers close to the wall (probably most of us), a wide-baffle speaker tends to reduce the negative impacts of such a placement.

Negatives -:
- more susceptible to diffraction effects so attention needs to be made to asymmetric driver placement or curving/beveling the baffle edges.
- Imaging is not as precise as a narrow baffle, but some would say that pinpoint imaging is not very realistic anyway.
- Size and weight (the main reason they lost favor with most manufacturers).

The best overall summation I've heard is that narrow baffles bring the performers into your room, wide baffles take you to the recording venue.

In an era of wide-screen TVs, I dont see a wide baffle speaker presenting much of a WAF issue.


http://www.gattiweb.com/images/apoll...easurement.jpg

Gattiweb

AllenB 5th November 2011 01:09 AM

Quote:

Originally Posted by David Gatti (Post 2770365)
The best overall summation I've heard is that narrow baffles bring the performers into your room, wide baffles take you to the recording venue.

Yes, or put another way, there are more reflections due to the wider directivity thus adding the room into the equation.

The concern is that after you consider the directivity of the tweeter, beaming of the woofer, and the baffle step, do they all line up across the spectrum to form a smooth 'homogenous' transition?

AllenB 5th November 2011 01:13 AM

Quote:

Originally Posted by David Gatti (Post 2770365)
- Imaging is not as precise as a narrow baffle,

Yes, in my opinion it can be more precise due to the reduced early reflections.

planet10 5th November 2011 01:27 AM

Quote:

Originally Posted by 454Casull (Post 2770148)
Wide-baffle speakers (some people call them monkey coffins)

Not so. Monkey coffin refers to any rectangular prism shaped box that resembles the kind of shape you would use as a coffin. The monkey part indicative of the size.

A good exmple

http://www.diyaudio.com/forums/attac...ormiva_iso.gif

dave

planet10 5th November 2011 01:33 AM

When i worked retail hifi we sold a ton of these BA. I remember a very memorable Sunday afternoon where we did a number of bsic mods to a set of A200s and transformed them.

dave


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